1. Field of the Invention
This invention relates to airbag passive restraint systems for vehicles and more particularly, to their inflatable bags of predetermined shape for restraining movement of a passenger seated on a front seat of the vehicle relative to the instrument panel by automatic and instantaneous inflation of the bag in the case of a collision accident. The invention is also concerned with methods for manufacturing the inflatable bags using a one-piece cut cloth having a polygonal figure. More specifically stated, the invention provides bags of the kind stated that assume a generally quadrilateral prismoidal shape and exhibit a "strapless strap effect" upon deployment thereof and the manufacture thereof.
2. Statement of Related Art
Airbag passive restraint systems are used as an auxiliary means for seat belt restraints and, in the event where a vehicle fitted with them collide at an impact of more than a predetermined magnitude, are operative to restrain a seated passenger against sudden movement and protect him by instantaneous inflation of the bag. In general, airbag restraint systems are made up of an inflator for releasing gas, an inflatable bag capable of inflating by the gas, a housing for surrounding and enclosing substantially hermetically the inflator and bag, and a sensor for detecting the predetermined impact and transmitting its electric signal to the inflator.
When an airbag restraint is actuated, gas released from the inflator by an electric signal is filled in the bag and housing to exert an inner pressure upon the surface of bag, which in turn causes the bag to deploy instantaneously.
In the past, airbag passive restraint systems for vehicles have been developed for mounting them not only to the steering wheel forward of a driver's seat, but also to the instrument panel forward of a front seat abreast it.
As inflatable bags for a front seat passenger, for example, a bag as illustrated in FIG. 26 has been known. The bag is made of a cloth and comprises a cylindrical body (41) sewed together and rounded triangular lateral portions (42) sewed to the cylindrical body at both sides thereof, the cylindrical body having, on its circumferential face, a square opening (43) which is an inlet for gas flow from the inflator. At the opening (43), four retainers (44)(45), partly made of the body cloth and partly of a different cloth, are sewed to the body (41) in a sack form. The retainer fittings (44,45) are fastened to a housing for bag through its retainer (not shown) to be inserted.
In configuring the bag by sewing work, however, it was necessary to sew together both marginal portions of the cylindrical body cloth and both outer perimeters of the lateral cloths that are curved and three-dimensional and consequently, time-consuming laborious manual work has been required, which was responsible for a bottleneck to automatization of sewing operation.
On the other hand, Japanese Patent Publication No. 52-4371 (1977) discloses a method for manufacturing a bag for airbag restraint assembly from a one-piece rectangular fabric as shown in FIGS. 27a and 27b. However, since the one-piece fabric is not applied with any suitable cutting according to a predetermined pattern, sewing and shaping of the fabric into a bag requires much skillful work, and the resulting bag has extra useless remnants, which make the weight of bag heavier and impart more impact to a seated passenger than necessary upon deploying. Further, the remnants are obstructive of sewing and make the automatization of sewing by the instrumentality of a machine difficult.
More specifically, when the fabric is shaped into a bag as shown in FIG. 27a by folding and sewing, triangular extensions (52) are formed at both sides of the base wall (50) and lateral marginal portions (53) with selvages are formed on side walls (51). The sewed body is then turned inside out to give a bag as shown in FIG. 27b. In order to mount the bag to a vehicle, further the sidewalls (51) of the bag are folded inwardly at their lower parts to be sewed to the free end (55) of the body wall (54). Consequently, bulky sewed places and overlapped portions are additionally formed.
Here, the more extensive is the area of the base wall (50) that is adapted to face a passenger, the more the triangular extensions (52) are enlarged whereas the larger is the taper degree of the lateral marginal portions (53), the more they are widened. These parts (52,53) and overlapped parts are useless for the restraint of a passenger that is a purpose proper of the airbag, because these increase in weight and take up a bulk and obstruct when the bag is folded and collapsed for housing in an instrument panel. The bag thus loses its flexibility to be stiff, and is disadvantageous for the restraint of a passenger.
In mass production of such a bag, a fabric of such a rectangular or square form is usually cut out from a fabric roll by making two longer sides and two shorter sides of a rectangle to coincide with the roll direction and width direction of the roll respectively or bringing a square into parallel with the roll direction. In either case, when a cut cloth thus obtained is then subjected to folding and sewing, the resulting seam lines are parallel with the fabric grain lines. This is not good for the construction of a bag since the inner pressure is exerted in parallel with the fabric grain lines on the bag.
If a one-piece cloth is cut out from a fabric foll obliquely to the roll direction for a good construction of bag, a longer roll width will be necessary than the existing roll width that is available from conventional looms, which necessitates new investment for an installation to that end. The width of the existing looms is usually on the order of 1.5 m whereas the perimeter length of a bag as viewed from the lateral side of a vehicle is ca. 2 m. Furthermore, the yield of one-piece cloth material is decreased, and the oblique cutting is thus uneconomical. From the aspect of sewing of a cloth, bias sewing, in which an angle is made between seam lines and grain lines of the fabric, affords a higher strength than parallel sewing wherein seam lines are parallel with the grain lines of fabric.
If a three-dimensional body is shaped from the one-piece fabric so that the triangular extensions (52), whose shape is determined by the lengths of the base wall (50) and two body walls (54), assumes an isosceles triangle, the resulting bag will be symmetrical relative to the stitching lines as viewed from a lateral side of a vehicle when mounted. If a bag is shaped in a manner forming the triangular extensions (52) of a scalene triangle and the same size of the base wall (50), then the base wall (50) will be inclined toward a passenger, which is disadvantageous for restraint performances to the passenger. Thus, the one-piece fabric imposes restrictions on the shape of a bag.
In general, it is desired from the respects of restraint performances, weight and cost that a bag have its lateral configuration as viewed from a lateral side of a vehicle, such that an upper face disposed along the windshield, a lower face disposed along the instrument panel and extending to the knees of a passenger and a front face disposed vis-a-vis to the passenger assume a triangular profile. As a consequence, a freedom in designing a bag of such a shape that will satisfy the foregoing conditions of vehicle is seeked and desired.
The disclosed method moreover requires a skillful art in sewing lapped sidewalls to the body wall and non-straight lines. The stitching lines are applied linearly over the whole length of the sidewalls (53) in the deployment direction of a bag, and consequently, it is further necessary to adopt a sewing technique for rendering the stitching places, on which the strength upon deployment concentrates, strong.
The known methods for manufacturing a bag for front seat passenger as well as the bags thus have posed many problems and had drawbacks.
In view of the prior art situations above, this invention has been accomplished by contriving a new one-piece cloth cut in a specified figure, from which a bag can be fashioned simply and easily.
Accordingly, a primary object of this invention is to provide a method for manufacturing an inflatable bag for airbag passive restraint systems for front seat passenger by the use of a one-piece cloth that enables rectilinear and plane sewing, thereby enabling automatic sewing work on a machine.
Another object of the invention is to provide a bag of the kind stated above and a method for manufacturing it which are characterized by the use of a one-piece cloth having such a figure that never produces useless parts when fashioned into a three-dimensional shape and requires a minimized number of sewing places and a possible smallest seam allowance whereby to yield the bag with such a light weight and a small bulk that it is readily housed in a housing for bag.
A still another object is to provide a bag and its manufacture which comprise using such a one-piece cloth that enables to impart a strap effect of regulating the flaring of the bag without the provision of any strap member.
A further object is to provide a bag and manufacturing thereof which enables a one-piece cloth after folding and sewing for fashioning of it into a three-dimensional shape to maintain its inherent or original flexibility, thereby producing a flexible bag.
A still further object is to provide a bag which is easily collapsible without any obstructs upon folding such as turn-up edges, local lapped portions, etc.
A further object is to provide a method for manufacturing a bag by the use of a one-piece cloth having such a figure that enables to enhance the degree of freedom in designing and changing the shape of the bag while considering its base (front) portion, lateral face portions, and upper and lower face portions in relation with vehicle components, e.g. an instrument panel, windshield, etc., the position and size of an opening of a housing for bag.
Yet further object is to provide a method of manufacturing a bag that enables simple sewing work and easy registering of sewing places without requiring any high skilled art, troublesome work, many steps, and much time.
These and other objects, features and advantages of this invention will become more apparent from the following description and the accompanying drawings.